In the 1980’S a major epidemiological study was performed by UCLA researchers focused on the population of Utah. This resulted in six publications. One study, the prevalence paper, has now been revisited recently with results indicating that the broadening of autism criteria with the shift from DSM III to DSM IV had a major impact on prevalence. In particular, on the prevalence of individuals with lower IQ’s.

Yes, the the DSM III missed a large number of individuals with low. IQ.

Here is the abstract from the 1990 study:

The UCLA-University of Utah epidemiologic survey of autism: Prevalence

Division of Mental Retardation and Child Psychiatry, University of California School of Medicine, Los Angeles.

The authors conducted an epidemiologic survey in Utah using a four-level ascertainment system, blind current diagnostic assessments, and DSM-III criteria. Of 483 individuals ascertained, 241 were diagnosed as having autism. The best estimate for the prevalence rate was 4 per 10,000 population. Autism was not associated with parental education, occupation, racial origin, or religion. Sixty-six percent of the autistic subjects scored below 70 on standardized IQ tests, and females scored proportionately lower than males. Twenty (9.7%) of 207 families had more than one autistic sibling, which supports the authors’ previous finding that there may be a familial subtype of autism

Abstract The purpose of the present study was to re-examine diagnostic data from a state-wide autism prevalence study (n = 489) conducted in the 1980s to investigate the impact of broader diagnostic criteria on autism spectrum disorder (ASD) case status. Sixty-four (59 %) of the 108 originally “Diagnosed Not Autistic” met the current ASD case definition. The average IQ estimate in the newly identified group (IQ = 35.58; SD = 23.01) was significantly lower than in the original group (IQ = 56.19 SD = 21.21; t = 5.75; p < .0001). Today’s diagnostic criteria applied to participants ascertained in the 1980s identified more cases of autism with intellectual disability. The current analysis puts this historic work into context and highlights differences in ascertainment between epidemiological studies performed decades ago and those of today.

Emphasis added.

This goes counter to the common perception that the expansion of diagnostic criteria was confined to adding so-called “higher functioning” autistics.

Comparing these results to the recent CDC results show that much of the increase in Utah was due to inclusion of higher IQ individuals. The recent prevalence estimate for Utah was 212/10,000 with most with IQ >70. One has to note that the prevalence estimate from the recent CDC report is roughly 20/10,000, about 5x higher than the UCLA report from 22 years ago. (further note that the CDC data for Utah are based on only 45 autistics so the error bars are very big).

It would be interesting to go through the screening process from the UCLA study to see how well they might have been able to capture individuals without intellectual disability.

This study doesn’t explain a substantial fraction of difference between the 1990 prevalence and the most recent estimate. It does point to a shift in diagnostic standards for low IQ individuals.

For the press conference, a small group of researchers were singled out and gave advance summaries of their work. David Amaral of U.C. Davis is the president of INSAR (the International Society for Autism Research) and hosted the press conference.

Amaral gave an introduction. This is the 10th IMFAR, and they returned to San Diego, where the first conference was held. The fist conference had 250 attendees. This one will have about 2,000. He stressed the focus on research into causes and treatment, the wide range of studies including environmental causation, and the strong passion and excitement of the researchers.

They found a number of interesting results. They looked at specific bundles of of nerves involved in long-range connectivity within the brain. Connectivity between the temperal lobe and limbic system (e.g. amygdala) are different amongst autistics from very early on. They looked at a measure called “fractional anisotropy”, or FA. For young autistics, FA is high. FA grows with time (it is a measure of maturity), but it grows slower than for non ASD kids. Result–FA is high for young (<30 month old) children, but low for older autistics. This is consistent with earlier work showing lower maturity (FA) for older autistics.

During questions, there was much dicussion of other aspects of Dr. Courchesne's research. There is a 2x increase in brain cells in the frontal cortex in very young autistics. This points to causation, at least for a large group, in very early events. There is also evidence from post mortem studies giving genetic evidence of dysregulation of functions that regularte cell number, cell migration, patternng of the brain, left/right brain symmetry and other factors of the brain. Not only are there differences in genetic expression and genetic pathways, but they are age dependent.

This brings up an important point for future research efforts. Researchers need to be aware that so many factors could be age dependent. Also, this gives some insight into possible developmental trajectories that the brain may undergoe. It was posited that the

The idea that FA starts out higher is new and presents a possible mechanism for different brain development in autistics. It was posited that the early structure of the autistic brain could result in the different developmental path.

On a related topic in the questions, I believe it was from David Amaral, it was noted that "precocious" brain growth is associated with regression. While it is known that large head diameters are common amongst autistics, changes in brain growth are observable as early in 4-6 months of age, well before the regression occurs.

And that's just the first person in the panel! I will get to the rest of the press conference shortly.

A long-awaited study of autism prevalence in Korea came out today in the American Journal of Psychiatry. Most of the information we have about autism prevalence comes from the US, the UK and Europe, so many were looking at this as the “Korean Study”. It is that, and very much more.

The title of the study is Prevalence of Autism Spectrum Disorders in a Total Population Sample. I expect the study will be gathering quite a lot of press as the results are quite remarkable. For one thing, the autism prevalence is estimated at 2.64%. That’s right, over double the current estimates in the United States and the U.K.. For another thing, most of the prevalence is for autistic students who were previously unidentified and unsupported.

The Simons Foundation blog, SFARI, has always had a good quality of articles. Lately it appears to me that the frequency of articles has increased. One recent article hits a subject that has been a focus of mine for some time: prevalence estimates and how they vary by culture and geography. In Researchers track down autism rates across the globe Virginia Hughes talks to a number of researchers working on expanding autism prevalence studies to more countries. Outside of the US and the UK, autism prevalence studies are somewhat rare. Until fairly recently, prevalence estimates outside of the US and Europe were basically nonexistent.

Ms. Hughes starts with this introduction:

In urban areas of South Korea, some families of children with developmental delays will go to great lengths to avoid a diagnosis of chapae, or autism. They think of it as a genetic mark of shame on the entire family, and a major obstacle to all of their children’s chances of finding suitable spouses.

The stigma is so intense that many Korean clinicians intentionally misdiagnose these children with aechak changae, or reactive detachment disorder — social withdrawal that is caused by extreme parental abuse or neglect.

This won’t come as a surprise for those who have read Roy Richard Grinker’sUnstrange Minds, where Prof. Grinker explores how autism is viewed in various parts of the world, including South Korea.

Prof. Grinker is interviewed, as is his collaborator Dr. Young Shin Kim, and Dr. Eric Fombonne.

Autism prevelance work has been performed or is ongoing in Mexico, South Korea, Brazil, India, South Africa and Oman. Since autism isn’t diagnosed through a biological test, variations in culture can have a significant impact on the test methods.

Ms. Hughes notes:

Language and culture may also affect the way this research is carried out. For instance, the Korean language uses an extensive array of suffixes that denote the relationship between the speaker and the subject. South Korean children with autism have trouble using these social markers, but the Western-based standard tests of autism, such as the Autism Diagnostic Observation Schedule (ADOS), don’t test for this.

Similarly, Grinker points out, healthy children from non-Western cultures may display a trait that ADOS counts as a symptom of autism. In South Korea, for example, making eye contact with an adult is not socially appropriate.

“This is why it’s pretty useful to have [anthropologists] who can translate diagnostic instruments that were designed in one culture and used in another,” Grinker says.

Rather than cut and paste the entire article I will point you back to SFARI for the full piece. It is well worth reading.

A couple of slap dash blog pieces appeared today both on the same subject – the so called autism epidemic. First off is Harold who writes about a series of interviews with David Kirby. David says:

<blockquote>It’s crazy that in this debate, we’re still debating whether autism numbers are actually going up or not, which is insanity to me. It’s people desperately clinging to this belief that autism is genetic, that it’s always been with us at this rate, that we’re just better at counting it, better at diagnosing it.</blockquote>

Harold claims David has ‘hit the nail on the head’ with this quote. I disagree with Harold and I disagree with David. Its far from insanity to examine a perfectly valid hypothesis. More later.

<blockquote>Why do I personally know so many young people with severe autism, whose symptoms can’t be ignored? How could we have just ignored these people in the past? Where are those misdiagnosed adults with classic autism—those with the same symptoms we see in so many children today?

I’m not talking about [Kristina] Chew’s autistic neighbor who was able to have a conversation with her, or [Paul] Offit’s people who are kind of ‘quirky.’ I mean adults who can’t talk, those in diapers, people who scream for hours and pound hours in walls and who constantly rock back and forth.</blockquote>

Dachel goes on to list several news reports which question the idea of there not being some kind of an epidemic. I disagree with her view and I disagree with the way she has reached her view.

Both Dachel and Harold (and David Kirby come to that) are claiming that epidemiology can be ursurped by individual experience – Dachel’s individual experience with ‘so many young people’ and David’s individual experience with the idea that people are desperately clinging on to some sort of belief in a genetic form of autism.

Now, casting aside the fact that the some of the forms of autism that we know about (Rett Syndrome etc) _are_ solely genetic we have to – as we do with _all_ forms of science, cast aside personal anecdote when making sweeping statements about a very large group of people. What we need to do instead is look at the science. So what does the science say?

Nothing. As far as I can see no firm case has been made that there either is or is not an autism epidemic. Why? Because the science hasn’t been done. It is maybe worth noting that it is the firm opinion of autism experts that a large part of any possible rise is due to:

a) Better diagnostic tools

b) More places at which to recieve a diagnosis

c) More awareness amongst clinicians of autism

d) Earlier diagnosis

e) Diagnostic substitution

f) Widening of diagnostic criteria

Experts such as Eric Fombonne, Roy Richard Grinker and Simon Baron-Cohen have all spoken about these ideas at length. However, that doesn’t make them right. There still seems to be no hard and fast science that says there is an autism epidemic or not.

A new paper from Eric Fombonne is in electronic print at the journal Pediatric Research. It will apparently be published in the paper version of the journal some time after April.

The title is ‘Epidemiology of pervasive developmental disorders’ and as the name suggests, Fombonne looks at all the available quality epidemiology he can find relating to PDD’s.

This article reviews the results of 43 studies published since 1966 that provided estimates for the prevalence of Pervasive Developmental Disorders, including Autistic Disorder, Asperger Disorder, Pervasive Developmental Disorder Not Otherwise Specified, and Childhood Disintegrative Disorder.

Combining all these categories together Fombonne presents a prevalence of 60-70/10,000.

For autistic disorder, Fombonne says:

The correlation between prevalence and year of publication was statistically significant and studies with prevalence
over 7/10,000 were all published since 1987. These findings point towards an increase in prevalence estimates in the last 15-20 years.

For PDD-NOS, Fombonne explains that it is next to impossible to get accurate prevalence rates as:

This group has been much less studied in previous epidemiological studies…

Again, for Aspergers, Fombonne says that AS specific epidemiological studies are sparse but, in something of a surprise:

By contrast, other recent autism surveys have consistently identified smaller numbers of children with AS than those with autism within the same survey. In 9 out of 10 such surveys, the ratio of autism to AS prevalence in each survey was above unity, suggesting that the prevalence of AS was consistently lower than that for autism. How much lower is difficult to establish from existing data, but a ratio of 3 or 4 to 1 would appear an acceptable, albeit conservative, conclusion based on this limited available evidence. This translates into a prevalence proportion for AS which would be ? to ¼ that of autism. We therefore used for subsequent calculations an estimate of 6/10,000 for AS, recognizing the strong limitations of available data on AS.

Lastly, for CDD:

Eight studies provided data on childhood disintegrative disorder (CDD). Prevalence estimates ranged from 0 to 9.2/100,000. The pooled estimate based on eight identified cases and a total surveyed population of 406,660 children, was 2.0/100,000. The upper-bound limit of the associated confidence interval (4.0/100,000) indicates that CDD is a very rare condition, with about 1 case to occur for every 103 cases of autistic disorder.

Fombonne then tackles the question everyone wants an answer to – is there an autism epidemic?

In order to answer this accurately, he explains that there has to be tight control over incidence estimates (the number of new cases occurring in a population over a period of time) and prevalence (the proportion of individuals in a population who suffer from a defined disorder). Failure to control these gives false results. Bearing this in mind, Fombonne goes through the five approaches taken so far to try and determine if theres an autism epidemic or not.

1) Referral Statistics.
Trends in time for referral statistics are not reliable. They fail to control for things such as referral patterns, availability of services, heightened public awareness, decreasing age at diagnosis and changes over time in diagnostic concepts and practices. An example of the issues from referral statistics is:

Strong evidence of “diagnostic switching” was produced in California and in all US states indicating that a relatively high proportion of children previously diagnosed as having mental retardation were now identified as having a PDD diagnosis. Decreased age at diagnosis has also been shown to contribute to the rising numbers of children diagnosed with PDD. In the UK, Jick and Kaye (62) have shown that the incidence of specific developmental disorders (including language disorders) decreased by about the same amount that the incidence of diagnoses of autism increased in boys born from 1990-1997. A more recent UK study has shown that up to 66% of adults previously diagnosed with developmental language disorders would meet diagnostic criteria for a broad definition of PDD.

2) Comparison of cross-sectional epidemiological surveys
If I’m understanding his point here (and please correct me if I’m not) Fombonne is saying that too many epidemiological studies are uniquely designed – not enough attempt to replicate a previous study – and hence:

The most convincing evidence that method factors could account for most of the variability in published prevalence estimates comes from a direct comparison of 8 recent surveys conducted in the UK and the USA. In each country, 4 surveys were conducted around the same year and with similar age groups. As there is no reason to expect huge between-area differences in prevalence, prevalence estimates should therefore be comparable within each country. However, there was a six-fold variation in prevalence for UK surveys, and a fourteen-fold variation in US figures. In each set of studies, high estimates derived from surveys where intensive population-based screening techniques were employed whereas lower prevalence proportions were obtained from studies relying on passive administrative methods for case finding. Since no passage of time was involved, the magnitude of these gradients in prevalence can only be attributed to differences in case identification methods across surveys.

3) Repeat surveys in defined geographical areas
So this is the opposite of the above – these are studies where they are being replicated as closely as is possible. However, the issue here is that there are simply not _enough_ of these studies to form a definite conclusion. However, it may be worth noting that in the two studies Fombonne highlighted as being carried out in exactly the same way in exactly the same place to exactly the same age cohort – but just at two different times one showed no increase in prevalence whilst the other showed no increase at 4 sites and an increase at 2 sites.

4) Successive birth cohorts
This means in very large surveys with a wide age range, if the proportion of people who have autism rises this _could_ be a rise in incidence and therefore a good hint that there is an epidemic. I say _could_ as other possible causes need to be ruled out first.

…two large French surveys [used this method]. The surveys included birth cohorts from 1972 to 1985…, and, pooling the data of both surveys, age-specific prevalence showed no upward trend.

A US survey _did_ show an upward trend but:

…the increase was not specific to autism. These analyses also showed a marked period effect that identified the early 1990s as the period where the prevalence estimates started to go up in all ages and birth cohorts, coinciding closely with the inclusion of PDDs in the federal Individual with Disabilities Educational Act (IDEA) funding and reporting mechanism in the US.

5) Incidence studies
The few incidence studies did show incidence trends rising over short periods of time. As noted in point 4) above, this _could_ be attributed to an autism epidemic. However –

…none of these studies investigations could determine the impact of changes over time in diagnostic criteria, improved awareness and service availability on the upward trend.

Contrary to what people who _want_ there to be an autism epidemic, these are non trivial reasons. It stands to reason that if (for example) Birmingham, UK – the countrys second city, goes from having zero service availability and no means of diagnosis in 1960 to having numerous types of service availability both publicly and privately funded and a _lot_ of means of diagnosis in 2000 there will be a _lot_ more autistic people in Birmingham. A hell of a lot. When we then consider that the diagnosis criteria has widened massively than we go from a hell of a lot more autistic people to a _whole hell_ of a lot. If we _also_ consider that people who used to carry one kind of diagnosis are now being swapped to autism then we go from a whole hell of a lot to a descriptive term beyond my ability. This isn’t even science – its basic common sense. The only issue is – ‘a whole hell of a lot’ is not a very accurate measurement.

Fombonne closes by saying that – based on the available data – we still cannot really say one way or the other if there has been an autism epidemic. Remember when you read the quote below that its _incidence_ that gives us an epidemic.

Current evidence does not strongly support the hypothesis of a secular increase in the incidence of autism but power to
detect time trends is seriously limited in existing datasets. Whilst it is clear that prevalence estimates have gone up over time, this increase most likely represents changes in the concepts, definitions, service availability and awareness of autistic-spectrum disorders in both the lay and professional public. To assess whether or not the incidence has increased, method factors that account for an important proportion of the variability in prevalence must be tightly controlled. The possibility that a true change in the underlying incidence has contributed to higher prevalence figures remains, however, to be adequately tested.

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